Partial Barrier Free Vias for Cobalt-Based Interconnects and Methods of Fabrication Thereof

ABSTRACT

Partial barrier-free vias and methods for forming such are disclosed herein. An exemplary interconnect structure of a multilayer interconnect feature includes a dielectric layer. A cobalt-comprising interconnect feature and a partial barrier-free via are disposed in the dielectric layer. The partial barrier-free via includes a first via plug portion disposed on and physically contacting the cobalt-comprising interconnect feature and the dielectric layer, a second via plug portion disposed over the first via plug portion, and a via barrier layer disposed between the second via plug portion and the first via plug portion. The via barrier layer is further disposed between the second via plug portion and the dielectric layer. The cobalt-comprising interconnect feature can be a device-level contact or a conductive line of the multilayer interconnect feature. The first via plug portion and the second via plug portion can include tungsten, cobalt, and/or ruthenium.

This application is a continuation application of U.S. Pat. ApplicationSerial No. 17/313,558, filed May 6, 2021, which is a divisionalapplication of U.S. Pat. Application Serial No. 16/399,697, filed Apr.30, 2019, which is a non-provisional application of and claims priorityto U.S. Provisional Pat. Application Serial No. 62/690,586, filed Jun.27, 2018, the entire disclosures of which are hereby incorporated hereinby reference.

BACKGROUND

The integrated circuit (IC) industry has experienced exponential growth.Technological advances in IC materials and design have producedgenerations of ICs, where each generation has smaller and more complexcircuits than the previous generation. In the course of IC evolution,functional density (i.e., the number of interconnected devices per chiparea) has generally increased while geometry size (i.e., the smallestcomponent (or line) that can be created using a fabrication process) hasdecreased. This scaling down process generally provides benefits byincreasing production efficiency and lowering associated costs.

Such scaling down has also increased the complexity of processing andmanufacturing ICs and, for these advances to be realized, similardevelopments in IC processing and manufacturing are needed. For example,as multilayer interconnect (MLI) features become more compact withever-shrinking IC feature size, interconnects of the MLI features areexhibiting increased contact resistance, which presents performance,yield, and cost challenges. It has been observed that higher contactresistances exhibited by interconnects in advanced IC technology nodescan significantly delay (and, in some situations, prevent) signals frombeing routed efficiently to and from IC devices, such as transistors,negating any improvements in performance of such IC devices in theadvanced technology nodes. Accordingly, although existing interconnectshave been generally adequate for their intended purposes, they have notbeen entirely satisfactory in all respects.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a fragmentary diagrammatic view of an integrated circuitdevice, in portion or entirety, according to various aspects of thepresent disclosure.

FIG. 2 is a flow chart of a method for fabricating an interconnectstructure of a multi-layer interconnect feature according to variousaspects of the present disclosure.

FIGS. 3A-3G are enlarged fragmentary diagrammatic views of a portion Aof the integrated circuit device of FIG. 1 , in portion or entirety,when implementing the method of FIG. 2 to fabricate an interconnectstructure of the integrated circuit device of FIG. 1 , according tovarious aspects of the present disclosure.

FIG. 4 , FIG. 5 , and FIG. 6 are enlarged fragmentary diagrammatic viewsof the portion A of different interconnect structures of the integratedcircuit device of FIG. 1 , in portion or entirety, that can arise whenimplementing the method of FIG. 2 , according to various aspects of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure relates generally to integrated circuit (IC)devices, and more particularly, to vias for multi-layer interconnectfeatures of IC devices.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

IC manufacturing process flow is typically divided into threecategories: front-end-of-line (FEOL), middle-end-of-line (MEOL), andback-end-of-line (BEOL). FEOL generally encompasses processes related tofabricating IC devices, such as transistors. For example, FEOL processescan include forming isolation features, gate structures, and source anddrain features (generally referred to as source/drain features). MEOLgenerally encompasses processes related to fabricating contacts toconductive features (or conductive regions) of the IC devices, such ascontacts to the gate structures and/or the source/drain features. BEOLgenerally encompasses processes related to fabricating a multilayerinterconnect (MLI) feature that interconnects IC features fabricated byFEOL and MEOL (referred to herein as FEOL and MEOL features orstructures, respectively), thereby enabling operation of the IC devices.

As IC technologies progress towards smaller technology nodes, BEOLprocesses are experiencing significant challenges. For example, advancedIC technology nodes require more compact MLI features, which requiressignificantly reducing critical dimensions of interconnects of the MLIfeatures (for example, widths and/or heights of vias and/or conductivelines of the interconnects). The reduced critical dimensions have led tosignificant increases in interconnect resistance, which can degrade ICdevice performance (for example, by increasing resistance-capacitance(RC) delay). Barrier-free vias have been proposed to replaceconventional vias to lower interconnect resistance for advanced ICtechnology nodes. Conventional vias include a via barrier layer and avia plug, where the via barrier layer is disposed between (1) the viaplug and an underlying interconnect feature (such as a device-levelcontact or a conductive line) and (2) the via plug and a dielectriclayer (for example, an interlayer dielectric (ILD) layer and/or acontact etch stop layer (CESL)) in which the via is disposed.Barrier-free vias eliminate the via barrier liner and/or any other linerlayer, such that the via plug directly contacts the underlyinginterconnect feature and the dielectric layer. Eliminating the viabarrier liner (along with other liner layers) increases a volume of thevia plug, lowering resistance.

Though barrier-free vias exhibit desirably low resistance, sometimes,via plug materials, such as tungsten, cobalt, and/or ruthenium, do notadhere well to the dielectric layer, such that gaps (or voids) existbetween the via plug and the dielectric layer. Poor adhesion of the viaplug to the dielectric layer (in particular, to sidewall surfaces and/orbottom surfaces of a via opening in which the via plug is formed) canlead to significant damage of the underlying interconnect feature,particularly when the underlying interconnect feature includes cobalt.For example, when polishing the via plug materials (for example, by achemical mechanical polishing (CMP) process), slurry used during thepolishing has been observed to penetrate an interface between the viaplug and the dielectric layer, seep through the gaps between the viaplug and the dielectric layer, and attack material of the underlyinginterconnect feature (in particular, cobalt), degrading its performance.Such performance degradation can be calamitous for device-level contactsthat include cobalt. For example, cobalt loss arising from exposure tochemicals during BEOL processing, such as CMP slurry (which is typicallyan acidic solution (in some implementations, having a pH value of about2)), have been observed to cause significant yield loss of underlyinginterconnect features, which is unacceptable for meeting shrinking ICtechnology node demands. Planarization-induced delamination or peelingof the via plug materials, particularly at a wafer periphery, have alsobeen observed as a result of the poor adhesion between the via plugmaterials and the dielectric layer.

The present disclosure discloses vias that protect underlyinginterconnect features (for example, device-level contacts and/orconductive lines), particularly underlying interconnect features thatinclude cobalt, from post-process damage and remedy many issues that mayarise with barrier-free vias. The partial barrier-free vias disclosedherein can prevent slurry used during planarization processes frompenetrating the interface between a via plug and a dielectric layer andreduce planarization-induced peeling. In some implementations, thepartial barrier-free vias disclosed herein include a floating viabarrier layer that enhances adhesion between an upper portion of thepartial barrier-free vias and a dielectric layer in which the partialbarrier-free vias are disposed. The floating via barrier layer isdisposed over a barrier-free via plug of the partial barrier-free via,such that the floating via barrier layer does not physically contact anunderlying interconnect feature, such as a device-level contact thatincludes cobalt. The via plug thus maintains sufficient volume of thepartial barrier-free vias, achieving low resistance characteristicssimilar to barrier-free vias. During fabrication of the partialbarrier-free vias, the planarization processes are performed on afloating, omega-shaped via barrier layer (from which the floating viabarrier layer is formed), which prevents damage to underlying conductivefeatures and/or reduces peeling of via plug material. Differentembodiments may have different advantages, and no particular advantageis required of any embodiment.

FIG. 1 is a fragmentary cross-sectional view of an IC device 10, inportion or entirety, according to various aspects of the presentdisclosure. IC device 10 can be included in a microprocessor, a memory,and/or other IC device. In some implementations, IC device 10 is aportion of an IC chip, a system on chip (SoC), or portion thereof, thatincludes various passive and active microelectronic devices, such asresistors, capacitors, inductors, diodes, p-type field effecttransistors (PFETs), n-type field effect transistors (NFETs),metal-oxide semiconductor field effect transistors (MOSFETs),complementary metal-oxide semiconductor (CMOS) transistors, bipolarjunction transistors (BJTs), laterally diffused MOS (LDMOS) transistors,high voltage transistors, high frequency transistors, other suitablecomponents, or combinations thereof. The transistors may be planartransistors or multi-gate transistors, such as fin-like FETs (FinFETs).FIG. 1 has been simplified for the sake of clarity to better understandthe inventive concepts of the present disclosure. Additional featurescan be added in IC device 10, and some of the features described belowcan be replaced, modified, or eliminated in other embodiments of ICdevice 10.

IC device 10 includes a substrate (wafer) 12. In the depictedembodiment, substrate 12 includes silicon. Alternatively oradditionally, substrate 12 includes another elementary semiconductor,such as germanium; a compound semiconductor, such as silicon carbide,gallium arsenide, gallium phosphide, indium phosphide, indium arsenide,and/or indium antimonide; an alloy semiconductor, such as silicongermanium (SiGe), GaAsP, AlInAs, AlGaAs, GaInAs, GaInP, and/or GaInAsP;or combinations thereof. In some implementations, substrate 12 includesone or more group III-V materials, one or more group II-IV materials, orcombinations thereof. In some implementations, substrate 12 is asemiconductor-on-insulator substrate, such as a silicon-on-insulator(SOI) substrate, a silicon germanium-on-insulator (SGOI) substrate, or agermanium-on-insulator (GOI) substrate. Semiconductor-on-insulatorsubstrates can be fabricated using separation by implantation of oxygen(SIMOX), wafer bonding, and/or other suitable methods. Substrate 12 caninclude various doped regions (not shown) configured according to designrequirements of IC device 10, such as p-type doped regions, n-type dopedregions, or combinations thereof. P-type doped regions (for example,p-type wells) include p-type dopants, such as boron, indium, otherp-type dopant, or combinations thereof. N-type doped regions (forexample, n-type wells) include n-type dopants, such as phosphorus,arsenic, other n-type dopant, or combinations thereof. In someimplementations, substrate 12 includes doped regions formed with acombination of p-type dopants and n-type dopants. The various dopedregions can be formed directly on and/or in substrate 12, for example,providing a p-well structure, an n-well structure, a dual-wellstructure, a raised structure, or combinations thereof. An ionimplantation process, a diffusion process, and/or other suitable dopingprocess can be performed to form the various doped regions.

An isolation feature(s) (not shown) is formed over and/or in substrate12 to isolate various regions, such as various device regions, of ICdevice 10. For example, isolation features define and electricallyisolate active device regions and/or passive device regions from eachother. Isolation features include silicon oxide, silicon nitride,silicon oxynitride, other suitable isolation material, or combinationsthereof. Isolation features can include different structures, such asshallow trench isolation (STI) structures, deep trench isolation (DTI)structures, and/or local oxidation of silicon (LOCOS) structures. Insome implementations, isolation features include STI features. Forexample, STI features can be formed by etching a trench in substrate 12(for example, by using a dry etch process and/or wet etch process) andfilling the trench with insulator material (for example, by using achemical vapor deposition process or a spin-on glass process). Achemical mechanical polishing (CMP) process may be performed to removeexcessive insulator material and/or planarize a top surface of isolationfeatures. In some embodiments, STI features include a multi-layerstructure that fills the trenches, such as a silicon nitride layerdisposed over an oxide liner layer.

Various gate structures are disposed over substrate 12, such as a gatestructure 20A, a gate structure 20B, and a gate structure 20C. In someimplementations, one or more of gate structures 20A-20C interpose asource region and a drain region, where a channel region is definedbetween the source region and the drain region. The one or more gatestructures 20A-20C engage the channel region, such that current can flowbetween the source/drain regions during operation. In someimplementations, gate structures 20A-20C are formed over a finstructure, such that gate structures 20A-20C each wrap a portion of thefin structure. For example, one or more of gate structures 20A-20C wrapchannel regions of the fin structure, thereby interposing source regionsand drain regions of the fin structure. Gate structures 20A-20C includemetal gate (MG) stacks, such as a metal gate stack 22A, a metal gatestack 22B, and a metal gate stack 22C. Metal gate stacks 22A-22C areconfigured to achieve desired functionality according to designrequirements of IC device 10, such that metal gate stacks 22A-22Cinclude the same or different layers and/or materials. In someimplementations, metal gate stacks 22A-22C include a gate dielectric anda gate electrode. The gate dielectric is disposed on substrate 12, andthe gate electrode is disposed on the gate dielectric. In someimplementations, the gate dielectric is conformally disposed on sidewallsurfaces and bottom surfaces of IC device 10 defining metal gate stacks22A-22C, such that the gate dielectric is generally u-shaped and has asubstantially uniform thickness. The gate dielectric includes adielectric material, such as silicon oxide, high-k dielectric material,other suitable dielectric material, or combinations thereof. High-kdielectric material generally refers to dielectric materials having ahigh dielectric constant, for example, greater than a dielectricconstant of silicon oxide (k ≈ 3.9). Exemplary high-k dielectricmaterials include hafnium, aluminum, zirconium, lanthanum, tantalum,titanium, yttrium, oxygen, nitrogen, other suitable constituent, orcombinations thereof. In some implementations, the gate dielectricincludes a multilayer structure, such as an interfacial layer including,for example, silicon oxide, and a high-k dielectric layer including, forexample, HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, ZrO₂, Al₂O₃,HfO₂-Al₂O₃, TiO₂, Ta₂O₅, La₂O₃, Y₂O₃, other suitable high-k dielectricmaterial, or combinations thereof. The gate electrode includes anelectrically conductive material. In some implementations, the gateelectrode includes multiple layers, such as one or more capping layers,work function layers, glue/barrier layers, and/or metal fill (or bulk)layers. A capping layer can include a material that prevents oreliminates diffusion and/or reaction of constituents between the gatedielectric and other layers of the gate electrode. In someimplementations, the capping layer includes a metal and nitrogen, suchas titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride(W₂N), titanium silicon nitride (TiSiN), tantalum silicon nitride(TaSiN), or combinations thereof. A work function layer includes aconductive material tuned to have a desired work function (such as ann-type work function or a p-type work function), such as n-type workfunction materials and/or p-type work function materials. P-type workfunction materials include TiN, TaN, Ru, Mo, Al, WN, ZrSi₂, MoSi₂,TaSi₂, NiSi₂, WN, other p-type work function material, or combinationsthereof. N-type work function materials include Ti, Al, Ag, Mn, Zr,TiAl, TiAlC, TaC, TaCN, TaSiN, TaAl, TaAlC, TiAlN, other n-type workfunction material, or combinations thereof. A glue/barrier layer caninclude a material that promotes adhesion between adjacent layers, suchas the work function layer and the metal fill layer, and/or a materialthat blocks and/or reduces diffusion between gate layers, such as suchas the work function layer and the metal fill layer. For example, theglue/barrier layer includes metal (for example, W, Al, Ta, Ti, Ni, Cu,Co, other suitable metal, or combinations thereof), metal oxides, metalnitrides (for example, TiN), or combinations thereof. A metal fill layercan include a suitable conductive material, such as Al, W, and/or Cu.

Metal gate stacks 22A-22C are fabricated according to a gate lastprocess, a gate first process, or a hybrid gate last/gate first process.In gate last process implementations, gate structures 20A-20C includedummy gate stacks that are subsequently replaced with metal gate stacks22A-22C. The dummy gate stacks include, for example, an interfaciallayer (including, for example, silicon oxide) and a dummy gate electrodelayer (including, for example, polysilicon). In such implementations,the dummy gate electrode layer is removed, thereby forming openings(trenches) in which metal gate stacks 22A-22C are formed. In someimplementations, the dummy gate stacks are formed before forming aninterlayer dielectric layer, and the dummy gate stacks are replaced withmetal gate stacks 22A-22C after forming the interlayer dielectric layer.Gate last processes and/or gate first processes can implement depositionprocesses, lithography processes, etching processes, other suitableprocesses, or combinations thereof. The deposition processes includeCVD, physical vapor deposition (PVD), atomic layer deposition (ALD),high density plasma CVD (HDPCVD), metal organic CVD (MOCVD), remoteplasma CVD (RPCVD), plasma enhanced CVD (PECVD), low-pressure CVD(LPCVD), atomic layer CVD (ALCVD), atmospheric pressure CVD (APCVD),plating, other suitable methods, or combinations thereof. Thelithography patterning processes include resist coating (for example,spin-on coating), soft baking, mask aligning, exposure, post-exposurebaking, developing the resist, rinsing, drying (for example, hardbaking), other suitable processes, or combinations thereof.Alternatively, the lithography exposure process is assisted,implemented, or replaced by other methods, such as maskless lithography,electron-beam writing, or ion-beam writing. The etching processesinclude dry etching processes, wet etching processes, other etchingprocesses, or combinations thereof.

Gate structures 20A-20C further include spacers 26A-26C, which aredisposed adjacent to (for example, along sidewalls of) metal gate stacks22A-22C, respectively. Spacers 26A-26C are formed by any suitableprocess and include a dielectric material. The dielectric material caninclude silicon, oxygen, carbon, nitrogen, other suitable material, orcombinations thereof (for example, silicon oxide, silicon nitride,silicon oxynitride, or silicon carbide). For example, in the depictedembodiment, a dielectric layer including silicon and nitrogen, such as asilicon nitride layer, can be deposited over substrate 12 andsubsequently anisotropically etched to form spacers 26A-26C. In someimplementations, spacers 26A-26C include a multilayer structure, such asa first dielectric layer that includes silicon nitride and a seconddielectric layer that includes silicon oxide. In some implementations,more than one set of spacers, such as seal spacers, offset spacers,sacrificial spacers, dummy spacers, and/or main spacers, are formedadjacent to metal gate stacks 22A-22C. In such implementations, thevarious sets of spacers can include materials having different etchrates. For example, a first dielectric layer including silicon andoxygen (for example, silicon oxide) can be deposited over substrate 12and subsequently anisotropically etched to form a first spacer setadjacent to metal gate stacks 22A-22C (or dummy metal gate stacks, insome implementations), and a second dielectric layer including siliconand nitrogen (for example, silicon nitride) can be deposited oversubstrate 12 and subsequently anisotropically etched to form a secondspacer set adjacent to the first spacer set. Implantation, diffusion,and/or annealing processes can be performed to form lightly doped sourceand drain (LDD) features and/or heavily doped source and drain (HDD)features in substrate 12 before and/or after forming spacers 26A-26C.

Epitaxial source features and epitaxial drain features (referred to asepitaxial source/drain features) are disposed in source/drain regions ofsubstrate 12. For example, a semiconductor material is epitaxially grownon substrate 12, forming epitaxial source/drain features 30 over asource region and a drain region of substrate 12. In the depictedembodiment, gate structure 20B interposes epitaxial source/drainfeatures 30, and a channel region is defined between epitaxialsource/drain features 30. Gate structure 20B and epitaxial source/drainfeatures 30 thus form a portion of a transistor of IC device 10. Gatestructure 20B and/or epitaxial source/drain features 30 are thusalternatively referred to as device features. In some implementations,epitaxial source/drain features 30 wrap source/drain regions of a finstructure. An epitaxy process can implement CVD deposition techniques(for example, vapor-phase epitaxy (VPE), ultra-high vacuum CVD(UHV-CVD), LPCVD, and/or PECVD), molecular beam epitaxy, other suitableSEG processes, or combinations thereof. The epitaxy process can usegaseous and/or liquid precursors, which interact with the composition ofsubstrate 12. Epitaxial source/drain features 30 are doped with n-typedopants and/or p-type dopants. In some implementations, where thetransistor is configured as an n-type device (for example, having ann-channel), epitaxial source/drain features 30 can be silicon-containingepitaxial layers or silicon-carbon-containing epitaxial layers dopedwith phosphorous, other n-type dopant, or combinations thereof (forexample, forming Si:P epitaxial layers or Si:C:P epitaxial layers). Insome implementations, where the transistor is configured as a p-typedevice (for example, having a p-channel), epitaxial source/drainfeatures 30 can be silicon-and-germanium-containing epitaxial layersdoped with boron, other p-type dopant, or combinations thereof (forexample, forming Si:Ge:B epitaxial layers). In some implementations,epitaxial source/drain features 30 include materials and/or dopants thatachieve desired tensile stress and/or compressive stress in the channelregion. In some implementations, epitaxial source/drain features 30 aredoped during deposition by adding impurities to a source material of theepitaxy process. In some implementations, epitaxial source/drainfeatures 30 are doped by an ion implantation process subsequent to adeposition process. In some implementations, annealing processes areperformed to activate dopants in epitaxial source/drain features 30and/or other source/drain regions of IC device 10 (for example, HDDregions and/or LDD regions).

In some implementations, silicide layers are formed on epitaxialsource/drain features 30. In some implementations, silicide layers areformed by depositing a metal layer over epitaxial source/drain features30. The metal layer includes any material suitable for promotingsilicide formation, such as nickel, platinum, palladium, vanadium,titanium, cobalt, tantalum, ytterbium, zirconium, other suitable metal,or combinations thereof. IC device 10 is then heated (for example,subjected to an annealing process) to cause constituents of epitaxialsource/drain features 30 (for example, silicon and/or germanium) toreact with the metal. The silicide layers thus include metal and aconstituent of epitaxial source/drain features 30 (for example, siliconand/or germanium). In some implementations, the silicide layers includenickel silicide, titanium silicide, or cobalt silicide. Any un-reactedmetal, such as remaining portions of the metal layer, is selectivelyremoved by any suitable process, such as an etching process. In someimplementations, the silicide layers and epitaxial source/drain features30 are collectively referred to as the epitaxial source/drain featuresof IC device 10.

A multilayer interconnect (MLI) feature 40 is disposed over substrate12. MLI feature 40 electrically couples various devices (for example,transistors, resistors, capacitors, and/or inductors) and/or components(for example, gate structures and/or source/drain features) of IC device10, such that the various devices and/or components can operate asspecified by design requirements of IC device 10. MLI feature 40includes a combination of dielectric layers and electrically conductivelayers (for example, metal layers) configured to form variousinterconnect structures. The conductive layers are configured to formvertical interconnect features (providing, for example, verticalconnection between features and/or vertical electrical routing), such ascontacts and/or vias, and/or horizontal interconnect features(providing, for example, horizontal electrical routing), such asconductive lines. Vertical interconnect features typically connecthorizontal interconnect features in different layers (or differentplanes) of MLI feature 40. During operation, the interconnect featuresare configured to route signals between the devices and/or thecomponents of IC device 10 and/or distribute signals (for example, clocksignals, voltage signals, and/or ground signals) to the devices and/orthe components of IC device 10. Though MLI feature 40 is depicted with agiven number of dielectric layers and conductive layers, the presentdisclosure contemplates MLI feature 40 having more or less dielectriclayers and/or conductive layers.

In FIG. 1 , MLI feature 40 includes one or more dielectric layers, suchas an interlayer dielectric layer 42 (ILD-0) disposed over substrate 12,an interlayer dielectric layer 44 (ILD-1) disposed over ILD layer 42, aninterlayer dielectric layer 46 (ILD-2) disposed over ILD layer 44, andan interlayer dielectric layer 48 (ILD-3) disposed over ILD layer 46.ILD layers 42-48 include a dielectric material including, for example,silicon oxide, silicon nitride, silicon oxynitride, TEOS formed oxide,PSG, BPSG, low-k dielectric material, other suitable dielectricmaterial, or combinations thereof. Exemplary low-k dielectric materialsinclude FSG, carbon doped silicon oxide, Black Diamond® (AppliedMaterials of Santa Clara, California), Xerogel, Aerogel, amorphousfluorinated carbon, Parylene, BCB, SiLK (Dow Chemical, Midland,Michigan), polyimide, other low-k dielectric material, or combinationsthereof. In the depicted embodiment, ILD layers 42-48 are dielectriclayers that include a low-k dielectric material (generally referred toas low-k dielectric layers). ILD layers 42-48 can include a multilayerstructure having multiple dielectric materials. MLI feature 40 canfurther include one or more contact etch stop layers (CESL) disposedover substrate 12, such as a CESL 52 disposed between ILD layer 42 andILD layer 44, a CESL 54 disposed between ILD layer 44 and ILD layer 46,and a CESL 56 disposed between ILD layer 46 and ILD layer 48. In someimplementations, a CESL (not shown) is also disposed between substrate12 and ILD layer 42. CESLs 52-56 include a material different than ILDlayers 42-48, such as a dielectric material that is different than thedielectric material of ILD layers 42-48. In the depicted embodiment,where ILD layers 42-48 include a low-k dielectric material, CESLs 52-56include silicon and nitrogen, such as silicon nitride or siliconoxynitride. ILD layers 42-48 and/or CESLs 52-56 are formed oversubstrate 12, for example, by a deposition process (such as CVD, PVD,ALD, HDPCVD, MOCVD, RPCVD, PECVD, LPCVD, ALCVD, APCVD, plating, othersuitable methods, or combinations thereof). In some implementations, ILDlayers 42-48 and/or CESLs 52-56 are formed by a flowable CVD (FCVD)process that includes, for example, depositing a flowable material (suchas a liquid compound) over substrate 12 and converting the flowablematerial to a solid material by a suitable technique, such as thermalannealing and/or ultraviolet radiation treating. Subsequent to thedeposition of ILD layers 42-48 and/or CESLs 52-56, a CMP process and/orother planarization process is performed, such that ILD layers 42-48and/or CESLs 52-56 have substantially planar surfaces for enhancingformation of overlying layers.

A device-level contact 60, a device-level contact 62, a device-levelcontact 64, a via 70, a via 72, a via 74, a conductive line 80, aconductive line 82, and a conductive line 84 are disposed in ILD layers42-48 to form interconnect structures. Device-level contacts 60-64 (alsoreferred to as local interconnects or local contacts) electricallycouple and/or physically couple IC device features to other conductivefeatures of MLI feature 40. For example, device-level contact 60 is ametal-to-poly (MP) contact, which generally refers to a contact to agate structure, such as a poly gate structure or a metal gate structure.In the depicted embodiment, device-level contact 60 is disposed on gatestructure 20B (in particular, metal gate stack 22B), such thatdevice-level contact 60 connects gate structure 20B to via 70.Device-level contact 60 extends through ILD layer 44 and CESL 52, thoughthe present disclosure contemplates embodiments where device-levelcontact 60 extends through more than one ILD layer and/or CESL of MLIfeature 40. In furtherance of the example, device-level contact 62 anddevice-level contact 64 are metal-to-device (MD) contacts, whichgenerally refer to contacts to a conductive region of IC device 10, suchas source/drain regions. In the depicted embodiment, device-levelcontact 62 and device-level contact 64 are disposed on respectiveepitaxial source/drain features 30, such that device-level contact 62and device-level contact 64 connect epitaxial source/drain features 30respectively to via 72 and via 74. Device-level contact 62 anddevice-level contact 64 extend through ILD layer 42, ILD layer 44, andCESL 52, though the present disclosure contemplates embodiments wheredevice-level contact 62 and/or device-level contact 64 extend throughmore than one ILD layer and/or CESL of MLI feature 40. In someimplementations, device-level contacts 60-64 are MEOL conductivefeatures that interconnect FEOL conductive features (for example, gatestructures 20A-20C and/or epitaxial source/drain features 30) to BEOLconductive features (for example, vias 70-74), thereby electricallyand/or physically coupling FEOL conductive features to BEOL conductivefeatures.

Vias 70-74 electrically couple and/or physically couple conductivefeatures of MLI feature 40 to one another. For example, via 70 isdisposed on device-level contact 60, such that via 70 connectsdevice-level contact 60 to conductive line 80; via 72 is disposed ondevice-level contact 62, such that via 72 connects device-level contact62 to conductive line 82; and via 74 is disposed on device-level contact64, such that via 74 connects device-level contact 64 to conductive line84. In the depicted embodiment, vias 70-74 extend through ILD layer 46and CESL 54, though the present disclosure contemplates embodimentswhere vias 70-74 extend through more than one ILD layer and/or CESL ofMLI feature 40. In some implementations, vias 70-74 are BEOL conductivefeatures that interconnect MEOL conductive features (for example,device-level contacts 60-64) to BEOL conductive features (for example,conductive lines 80-84), thereby electrically and/or physically couplingMEOL conductive features to BEOL conductive features. In someimplementations, MLI feature 40 further includes vias that are BEOLconductive features that interconnect BEOL conductive features indifferent ILD layers to one another, such as conductive lines 80-84 toconductive lines (not shown) disposed in other ILD layers (not shown)overlying ILD layers 42-48, thereby electrically and/or physicallycoupling BEOL conductive features of IC device 10.

Device-level contacts 60-64, vias 70-74, and conductive lines 80-84include any suitable conductive material, such as Ta, Ti, Al, Cu, Co,TaN, TiN, and/or other suitable conductive materials. Device-levelcontacts 60-64, vias 70-74, and conductive lines 80-84 are formed bypatterning ILD layers 42-48 and/or CESLs 52-56. Patterning ILD layers42-48 and CESLs 52-56 can include lithography processes and/or etchingprocesses to form openings (trenches), such as contact openings and/orline openings in respective ILD layers 42-48 and/or CESLs 52-56. In someimplementations, the lithography processes include forming a resistlayer over respective ILD layers 42-48 and/or CESLs 52-56, exposing theresist layer to pattern radiation, and developing the exposed resistlayer, thereby forming a patterned resist layer that can be used as amasking element for etching opening(s) in respective ILD layers 42-48and/or CESLs 52-56. The etching processes include dry etching processes,wet etching processes, other etching processes, or combinations thereof.Thereafter, the opening(s) are filled with one or more conductivematerials. The conductive material(s) can be deposited by PVD, CVD, ALD,electroplating, electroless plating, other suitable deposition process,or combinations thereof. Thereafter, any excess conductive material(s)can be removed by a planarization process, such as a CMP process,thereby planarizing a top surface of ILD layers 42-48, CESLs 52-56,device-level contacts 60-64, vias 70-74, and/or conductive lines 80-84.

FIG. 2 is a flow chart of a method 100 for fabricating an interconnectstructure of an MLI feature according to various aspects of the presentdisclosure. FIGS. 3A-3G are enlarged fragmentary diagrammatic views of aportion A of IC device 10, in portion or entirety, when implementingmethod 100 of FIG. 2 to fabricate the interconnect structure of the MLIfeature according to various aspects of the present disclosure. Theinterconnect structure of FIG. 2 and FIGS. 3A-3G includes a via, such asvia 72, configured to protect underlying conductive features of the MLIfeature, such as underlying MEOL features and/or underlying BEOLfeatures, from damage during subsequent processing, as described herein.FIG. 2 and FIGS. 3A-3G have been simplified for the sake of clarity tobetter understand the inventive concepts of the present disclosure.Additional steps can be provided before, during, and after method 100,and some of the steps described can be moved, replaced, or eliminatedfor additional embodiments of method 100. Additional features can beadded in the interconnect structure depicted in portion A, and some ofthe features described below can be replaced, modified, or eliminated inother embodiments of the interconnect structure depicted in portion A.

At block 110, a first interconnect feature of an MLI feature is formedin a first dielectric layer. In some implementations, the firstinterconnect feature is a MEOL feature, such as a device-level contactof the MLI feature (for example, one of device-level contacts 60-64).Alternatively, in some implementations, the first interconnect featureis a BEOL feature, such as a conductive line of the MLI feature (forexample, one of conductive lines 80-84). The first interconnect featureincludes cobalt. For example, turning to FIG. 3A, device-level contact62 is formed in ILD layer 44. Device-level contact 62 includes cobalt.In some implementations, a volume of device-level contact 62 includes atleast 20% cobalt. For example, device-level contact 62 includes cobaltor cobalt alloy (for example, including titanium, tungsten, nickel,phosphorous, boron, aluminum, tantalum, other suitable cobalt alloyingconstituent, or combinations thereof). In some implementations, formingdevice-level contact 62 includes performing a lithography and etchingprocess to form a contact opening in ILD layer 44 (which further extendsinto CESL 52 and ILD layer 42 (not shown)), filling the contact openingwith a cobalt-containing material, and performing a planarizationprocess that removes excess cobalt-containing material, such that thecobalt-containing material and the ILD layer 44 have substantiallyplanar surfaces. The contact opening has sidewalls defined by ILD layer44 (along with CESL 52 and ILD layer 42) and a bottom defined by an ICfeature, such as epitaxial source/drain feature 30 (not shown). Thecobalt-containing material is formed by a deposition process (forexample, PVD, CVD, ALD, or other suitable deposition process) and/orannealing process. In some implementations, a cobalt precursor usedduring the deposition process is cyclopentadienyl cobalt dicarbonyl(CpCo(CO)₂), dicobalt hexcarbonyl tertbutylacctylene (CCTBA), cobalttricarbonyl nitrosyl (Co(CO)₃NO), bis(cyclopentadienyl)cobalt(Co(C₅H₅)₂,CpCo(CO)₂), bis(ethylcyclopentadienyl)cobalt (C₁₄H₁₈Co),bis(pentamethylcyclopentadienyl)cobalt (C₂₀H₃₀Co), cobalttris(2,2,6,6-tetramethyl-3,5-heptanedionate)(Co(OCC(CH₃)₃CHCOC(CH₃)₃)₃), bis(ethylcyclopentadienyl)cobalt(C₁₄H₁₈Co), other suitable cobalt precursor, or combinations thereof. Insome implementations, device-level contact 62 includes a bulk layer(also referred to as a device-level plug) that consists essentially ofcobalt or cobalt alloy. In some implementations, device-level contact 62includes a barrier layer, an adhesion layer, and/or other suitable layerdisposed between the bulk layer and ILD layer 44 (along with CESL 52 andILD layer 42). In such implementations, the barrier layer and/or theadhesion layer conform to the contact opening, such that the barrierlayer and/or the adhesion layer are disposed on ILD layer 44 (along withCESL 52, ILD layer 42, and epitaxial source/drain feature 30) and thebulk layer is disposed on the barrier layer and/or the adhesion layer.In some implementations, the barrier layer, the adhesion layer, and/orother suitable layer include titanium, titanium alloy (for example,TiN), tantalum, tantalum alloy (for example, TaN), other suitableconstituent, or combinations thereof.

At block 120, a via opening is formed in a second dielectric layer,wherein the via opening exposes the first interconnect feature. Forexample, turning to FIG. 3B, a via opening 122 is formed in ILD layer 46(and, in some implementations, CESL 54) by a patterning process toexpose device-level contact 62. In the depicted embodiment, via opening122 extends vertically through ILD 46 and CESL 54. Via opening 122includes a sidewall 124 (defined by ILD 46 and CESL 54), a sidewall 126(defined by ILD 46 and CESL 54), and a bottom 128 (defined bydevice-level contact 62) that extends between sidewall 124 and sidewall126. In some implementations, a depth D of via opening 122 is about 10nm to about 50 nm. In some implementations, forming via opening 122includes forming a dielectric layer over device-level contact 62 and ILDlayer 44 (here, ILD layer 46) and patterning the dielectric layer toinclude an opening that exposes device-level contact 62, such as a topsurface 129 of device-level contact 62. In some implementations, a CVDprocess is performed to deposit a low-k dielectric material overdevice-level contact 62 and ILD layer 44, thereby forming ILD layer 46.CESL 54 can be formed over ILD 44 before forming ILD layer 46, thoughthe present disclosure contemplates embodiments that omit CESL 54. CESL54 includes a material having a different etching characteristic than amaterial of ILD layer 46, such as silicon nitride. ILD layer 46 (andCESL 54) can be patterned by lithography processes and/or etchingprocesses. For example, forming via opening 122 includes performing alithography process to form a patterned resist layer (not shown) overILD layer 46 and performing an etching process to transfer a patterndefined in the patterned resist layer to ILD layer 46. The lithographyprocess can include forming a resist layer on ILD layer 46 (for example,by spin coating), performing a pre-exposure baking process, performingan exposure process using a mask, performing a post-exposure bakingprocess, and performing a developing process. During the exposureprocess, the resist layer is exposed to radiation energy (such asultraviolet (UV) light, deep UV (DUV) light, or extreme UV (EUV) light),where the mask blocks, transmits, and/or reflects radiation to theresist layer depending on a mask pattern of the mask and/or mask type(for example, binary mask, phase shift mask, or EUV mask), such that animage is projected onto the resist layer that corresponds with the maskpattern. Since the resist layer is sensitive to radiation energy,exposed portions of the resist layer chemically change, and exposed (ornon-exposed) portions of the resist layer are dissolved during thedeveloping process depending on characteristics of the resist layer andcharacteristics of a developing solution used in the developing process.After development, the patterned resist layer includes a resist patternthat corresponds with the mask. The etching process uses the patternedresist layer as an etch mask to remove portions of ILD layer 46 and CESL54, thereby exposing device-level contact 62 (for example, a bulk layerof device-level contact 62 that includes cobalt). In someimplementations, ILD layer 46 is used as etching mask when removingportions of CESL 54. The etching process can include a dry etchingprocess (for example, a reactive ion etching (RIE) process), a wetetching process, other suitable etching process, or combinationsthereof. In some implementations, various selective etching processesare performed to form via opening 122. After the etching process, thepatterned resist layer is removed from ILD layer 46, for example, by aresist stripping process. Alternatively, the exposure process can beimplemented or replaced by other methods, such as maskless lithography,electron-beam writing, ion-beam writing, and/or nanoimprint technology.

At block 130, a first via bulk layer (also referred to as a first viaplug) is formed in the via opening. For example, turning to FIG. 3C, avia bulk layer 132 is formed in via opening 122. Via bulk layer 132partially fills via opening 122, such that via bulk layer 132 has athickness T1 that is less than depth D. In some implementations,thickness T1 is less than about 50 nm (for example, about 5 nm to about49 nm). In the depicted embodiment, via bulk layer 132 is disposeddirectly on exposed top surface 129 of device-level contact 62 and aportion of sidewalls 124, 126 defined by ILD layer 46 and CESL 54. Aremaining (unfilled) portion of via opening 122 has a depth D′, which isdefined between a top surface of ILD layer 46 and a top surface 134 ofvia bulk layer 132. In some implementations, depth D′ is about 1 nm toabout 45 nm. In the depicted embodiment, via bulk layer 132 includestungsten, tungsten alloy, ruthenium, ruthenium alloy, cobalt, or cobaltalloy. In some implementations, via bulk layer 132 includes tungsten,ruthenium, cobalt, copper, aluminum, iridium, palladium, platinum,nickel, other low resistivity metal constituent, alloys thereof, orcombinations thereof. In some implementations, a material of via bulklayer 132, such as copper, may necessitate a liner layer configured toprevent metal constituents of via bulk layer 132 from diffusing into ILDlayer 46. Via bulk layer 132 is formed by a bottom-up depositionprocess, which generally refers to a deposition process that fills anopening from bottom to top (which can be referred to as bottom-up fillof the opening). In some implementations, the bottom-up depositionprocess includes configuring the various parameters of the depositionprocess to selectively grow via bulk material from metal surfaces (here,bottom 128 of via opening 122 defined by exposed top surface 129 ofdevice-level contact 62) while limiting (or preventing) growth of thevia bulk material from dielectric surfaces (here, sidewalls 124, 126defined by ILD layer 46 and CESL 54 and a top surface of ILD layer 46).Such can be referred to as a selective deposition process. For example,forming via bulk layer 132 includes tuning various parameters of adeposition process, such as a CVD process, to selectively grow tungsten,ruthenium, or cobalt, from exposed top surface 129 of device-levelcontact 62 while limiting (or preventing) growth of the tungsten,ruthenium, or cobalt from ILD layer 46 and/or CESL 54. The variousdeposition parameters that can be tuned include deposition precursors(for example, metal precursors and/or reactants), deposition precursorflow rates, deposition temperature, deposition time, depositionpressure, source power, radio frequency (RF) bias voltage, RF biaspower, other suitable deposition parameters, or combinations thereof. Inanother example, forming via bulk layer 132 includes performing anALD-cyclic process, where a number of ALD cycles is tuned to controlthickness T1 of via bulk layer 132, such as a ruthenium layer. Thedeposition process is PVD, CVD, ALD, electroplating, electrolessplating, other suitable deposition process, or combinations thereof.Thickness T1 and depth D can be tuned to achieve a ratio of thickness T1to depth D that enhances the bottom-up deposition process. For example,in some implementations, a ratio of thickness T1 to depth D (T1/D) isabout 1 to about 20. Alternatively, in some implementations, via bulklayer 132 is formed by depositing a via bulk material that completelyfills via opening 122 (not necessarily in a bottom-up fashion) andetching back the via bulk material until achieving a desired thickness(for example, thickness T1) of via bulk layer 132 and/or a desired depthof the remaining (unfilled) portion of via opening 122 (for example,depth D′). In some implementations, the etching back can remove any viabulk material deposited over the top surface of ILD layer 46. Thedepositing and etching back can be implemented by any suitable process,such as those described herein.

At block 140, a via barrier layer (also referred to as a via linerlayer) is formed over the via bulk layer in the via opening. Forexample, turning to FIG. 3D, a via barrier layer 142 is formed in viaopening 122. Via barrier layer 142 partially fills via opening 122. Inthe depicted embodiment, via barrier layer 142 is disposed directly onportions of via bulk layer 132 and ILD layer 46 that define theremaining (unfilled) portion of via opening 122 (here, top surface 134of via bulk layer 132 and remaining portions of sidewalls 124, 126defined by ILD layer 46). As deposited, via barrier layer 142 exhibitsan omega shape and does not physically contact device-level contact 62(in contrast to conventional via barrier layers), such that via barrierlayer 142 “floats” within via opening 122. Via barrier layer 142 is thusreferred to as a “floating” omega-shaped via barrier layer. Depth D′ ofthe remaining (unfilled) portion of via opening 122 is reduced to adepth D¹′, which is defined between a top surface 144 of via barrierlayer 142 and the top surface of ILD layer 46. In some implementations,depth D¹′is about 1 nm to about 10 nm. Via barrier layer 142 isconformally deposited by PVD, CVD, ALD, electroplating, electrolessplating, other suitable deposition process, or combinations thereof,such that via barrier layer 142 has a thickness T2 that is substantiallyuniform over exposed surfaces of the interconnect structure. In thedepicted embodiment, thickness T2 is less than depth D′, and a sum ofthickness T1 and thickness T2 is less than depth D. In someimplementations, thickness T2 is about 1 nm to about 10 nm. Via barrierlayer 142 includes a material that promotes adhesion between adielectric material (here, ILD layer 46) and a subsequently formed metalmaterial for filling via opening 122. For example, via barrier layer 142includes titanium, titanium alloy, tantalum, tantalum alloy, cobalt,cobalt alloy, ruthenium, ruthenium alloy, molybdenum, molybdenum alloy,other suitable constituent configured to promote and/or enhance adhesionbetween a metal material and a dielectric material, or combinationsthereof. In the depicted embodiment, via barrier layer 142 includestantalum and nitrogen (for example, tantalum nitride) or titanium andnitrogen (for example, titanium nitride). In some implementations, viabarrier layer 142 includes more than is a via barrier multi-layer. Forexample, via barrier layer 142 includes a first sub-layer that includestitanium and a second sub-layer that includes titanium nitride. Inanother example, via barrier layer 142 includes a first sub-layer thatincludes tantalum and a second sub-layer that includes tantalum nitride.

At block 150, a second via bulk layer (also referred to as a second viaplug) is formed over the via barrier layer in the via opening. Forexample, turning to FIG. 3E, a via bulk layer 152 is formed in viaopening 122, such that via bulk layer 152 fills any remaining (unfilled)portion of via opening 122. In the depicted embodiment, via bulk layer152 is disposed directly on top surface 144 of via barrier layer 142. Inthe depicted embodiment, via bulk layer 152 includes tungsten, tungstenalloy, ruthenium, ruthenium alloy, cobalt, or cobalt alloy. In someimplementations, via bulk layer 152 includes tungsten, ruthenium,cobalt, copper, aluminum, iridium, palladium, platinum, nickel, otherlow resistivity metal constituent, alloys thereof, or combinationsthereof. In some implementations, a metal material of via bulk layer 152is the same as a metal material. In some implementations, a metalmaterial of via bulk layer 152 is different than a metal material. Viabulk layer 152 is formed by a non-selective deposition process. Forexample, a blanket deposition process, such as CVD, is performed todeposit via bulk material over via barrier layer 142, thereby formingvia bulk layer 152. In some implementations, the blanket depositionprocess is PVD, ALD, electroplating, electroless plating, other suitabledeposition process, or combinations thereof.

At block 160, a planarization process is performed, such that aremainder of the first via bulk layer, the via barrier layer, and thesecond via bulk layer form a via (an interconnect feature) of the MLIfeature. For example, turning to FIG. 3F, a CMP process and/or otherplanarization process is performed to remove excess via bulk layer 152and/or via barrier layer 142 (such as that disposed over the top surfaceof ILD layer 46), resulting in a via 72. Via 72 includes via bulk layer132, via barrier layer 142, and via bulk layer 152 having a thickness T3(which combine to fill via opening 122). In some implementations,thickness T3 is about equal to D^(1′) and less than thickness T1. Forexample, in some implementations, thickness T3 is about 1 nm to about 10nm. The CMP process can planarize a top surface of via 72, such that atop surface of ILD layer 46 and a top surface of via 72 aresubstantially planar surfaces. Forming floating, omega-shaped viabarrier layer 142 over via bulk layer 132 (FIG. 3E) improves adhesionbetween an upper portion of via 72 and ILD layer 46 (and/or a CESL),significantly reducing (and, in some implementations, eliminating) anygaps between via 72 and ILD layer 46. Slurry from the planarizationprocess is thus prevented from seeping to underlying device-levelcontact 62, preventing or reducing corrosion (damage) of underlyingdevice-level contact 62 during the planarization process and/or othersubsequent processing. The enhanced adhesion provided between the upperportion of via 72 and ILD layer by floating, omega-shaped via barrierlayer 142 can further prevent planarization-induced peeling.

Via bulk layer 132 and via bulk layer 152 can collectively be referredto as a via plug, where via bulk layer 132 is a first via plug portionand via bulk layer 152 is a second via plug portion. In the depictedembodiment, via 72 has a barrier-free via portion 162A, where no barrierlayer exists between the via plug (here, via bulk layer 132) and an ILDlayer and/or a CESL (here, ILD layer 46 and CESL 54), and a barrier viaportion 162B, where a barrier layer (here, via barrier layer 142) isdisposed between the via plug (here, via bulk layer 152) and the ILDlayer and/or the CESL (here, ILD layer 46). Via barrier layer 142 thusonly partially lines sidewalls of via 72. In FIG. 3F, via barrier layer142 lines a bottom surface of via bulk layer 152, sidewalls of via bulklayer 152, and a top surface of via bulk layer 132, but does not line abottom surface or sidewalls of via bulk layer 132. Since via bulk layer132 is disposed between via barrier layer 142 and device-level contact62, via barrier layer 142 floats within via 72 and does not physicallycontact device-level contact 62. Accordingly, a volume of the via plug,such as via bulk layer 132 and/or via bulk layer 152, is maintainedsufficiently high and via barrier layer 142 has minimal impact on aresistance of via 72, such that via 72 exhibits low resistance, and insome implementations, exhibits resistances similar to that ofbarrier-free vias. In some implementations, via barrier layer 142constitutes less than about 2% of a volume of via 72, via bulk layer 152constitutes about 1% to about 10% of the volume of via 72, and via bulklayer 132 constitutes about 90% to about 99% of the volume of via 72. Insome implementations, to maximize via plug volume, via barrier layer 142is disposed in a topmost portion of via 72 having a thickness of about 1nm to about 10 nm.

In furtherance of the depicted embodiment, via bulk layer 142 hasportions A and a portion B disposed between portions A, where portions Aand portion B combine to form a substantially U-shaped via bulk layer142. Portions A line ILD layer 46 and portion B lines top surface 134 ofvia bulk layer 132. Portions A have thickness T2 and portion B hasthickness T2, such that via bulk layer 132 has a substantially uniformthickness in via 72. Top surface of portion B is lower than top surfacesof portions A. In the depicted embodiment, top surfaces of portions Aand portion B of via bulk layer 142 are substantially planar. Sidewallsof via bulk layer 152 are lined by portions A of via barrier layer 142and the bottom of via bulk layer 152 is lined by portion B, such thatvia bulk layer 152 is partially surrounded by via barrier layer 142 onthree sides. A width (W₁₅₂) of via bulk layer 152 is less than a width(W₁₃₂) of via bulk layer 132. In some implementations, a width of viabulk layer 152 is about equal to a width of via bulk layer 132 minusthickness T2 of portions A of via barrier layer 142 (in other words,W₁₅₂ = W₁₃₂ - T2). A thickness of via bulk layer 132 is greater than athickness of via bulk layer 152 (in other words, T1 > T3) and athickness of via barrier layer 142 (in other words, T1 > T2). In someimplementations, a ratio of thickness T1 to thickness T2 (T1:T2) isabout 5:1 to about 25:1. In some implementations, a thickness of viabulk layer 132 is greater than a sum of a thickness of via bulk layer132 and a thickness of via barrier layer 142 (in other words, T1 > T2 +T3). In some implementations, a ratio of thickness T1 to a sum ofthickness T2 and thickness T3 (T1:T2+T3) is about 2.5:1 to about 12.5:1.In the depicted embodiment, via bulk layer 132 has a rectangular-shapedcross-section. For example, via bulk layer 132 has a substantiallyplanar bottom surface, a substantially planar top surface, andsubstantially planar sidewalls. In some implementations, sidewalls ofvia 72 are tapered, such that sidewalls of via bulk layer 132, viabarrier layer 142, and/or via bulk layer 152 are tapered. Via bulk layer132 may thus have a trapezoidal-shaped cross-section. In suchimplementations, thicknesses of via bulk layer 132 and/or via bulk layer152 decrease from their top surfaces to their bottom surfaces.

At block 170, a second interconnect feature of the MLI feature is formedin a third dielectric layer. The second interconnect feature is a BEOLfeature, such as a conductive line of the MLI feature (for example, oneof conductive lines 80-84). For example, turning to FIG. 3G, conductiveline 82 is formed in ILD layer 48. Conductive line 82 includes tungsten,ruthenium, cobalt, copper, aluminum, iridium, palladium, platinum,nickel, other low resistivity metal constituent, alloys thereof, orcombinations thereof. In some implementations, forming conductive line82 includes performing a lithography and etching process to form acontact opening in ILD layer 48 (which further extends into CESL 56),filling the contact opening with a conductive material, and performing aplanarization process that removes excess conductive, such that theconductive and the ILD layer 48 have substantially planar surfaces. Thecontact opening has sidewalls defined by ILD layer 48 (along with CESL56) and a bottom defined by via 72. The conductive material is formed bya deposition process (for example, PVD, CVD, ALD, or other suitabledeposition process) and/or annealing process. In some implementations,conductive line 82 includes a bulk layer (also referred to as aconductive plug). In some implementations, conductive line 82 includes abarrier layer, an adhesion layer, and/or other suitable layer disposedbetween the bulk layer and ILD layer 48 (along with CESL 56). In suchimplementations, the barrier layer and/or the adhesion layer conform tothe contact opening, such that the barrier layer and/or the adhesionlayer are disposed on ILD layer 48 (along with CESL 56) and the bulklayer is disposed on the barrier layer and/or the adhesion layer. Insome implementations, the barrier layer, the adhesion layer, and/orother suitable layer include titanium, titanium alloy (for example,TiN), tantalum, tantalum alloy (for example, TaN), other suitableconstituent, or combinations thereof. In the depicted embodiment,conductive line 82 has a rectangular-shaped cross-section. For example,conductive line 82 has a substantially planar bottom surface, asubstantially planar top surface, and substantially planar sidewalls. Insome implementations, sidewalls of conductive line 82 are tapered, suchthat a thickness of conductive line 82 decreases from a top surface ofILD layer 48 to the top surface of ILD layer 46. In furtherance of thedepicted embodiment, conductive line 82 physically contacts ILD layer46, via barrier layer 142, and via bulk layer 152.

Device-level contact 62, via 72, and conductive line 82 combine to forman interconnect structure 172 of MLI feature 40. Via 72 extendsvertically through ILD layer 46 and CESL 54 to physically and/orelectrically couple interconnect features in different levels (orlayers) of MLI feature 40 - here, device-level contact 62 (disposed in acontact layer of MLI feature 140) and conductive line 82 (disposed in ametal-1 (M1) layer of MLI feature 40). At block 180, fabrication cancontinue to complete fabrication of the MLI feature, such as MLI feature40. For example, additional levels of MLI feature 40 can be formed overthe M1 layer, such as an M2 layer to an Mn layer, where n represents anumber of metal layers in MLI feature 40 and each of M2 layer to Mnlayer include conductive lines, similar to conductive lines 80-84disposed in a dielectric material. Vias, similar to vias 70-74, can befabricated to connect adjacent metal layers, such as M2 layer to Mnlayer. In some implementations, one or more of the vias may connectnon-adjacent metal layers.

The present disclosure contemplates embodiments where via bulk layer 152and/or via barrier layer 142 are partially or fully removed from viaopening 122 by the planarization process. For example, parameters of theplanarization process, such as the CMP process, can be configured tomodify a profile of via barrier layer 142 and/or via bulk layer 152 asdesired. In some implementations, the parameters of the planarizationprocess are tuned to achieve desired top surface configurations and/orthickness configurations of via barrier layer 142 and/or via bulk layer152. Turning to FIGS. 4-6 , FIGS. 4-6 are enlarged fragmentarydiagrammatic views of the portion A of IC device 10, in portion orentirety, according to various aspects of the present disclosure. InFIG. 4 , the planarization process implemented in method 100 of FIG. 2fully removes via bulk layer 152 and partially removes via barrier layer142, such that via 72 does not include via bulk layer 152. Theplanarization process modifies a top surface of via barrier layer 142.For example, portion B of via barrier layer 142 has a concave topsurface, such that a thickness of a center of portion B is less than athickness of edges of portion B. In some implementations, a thickness ofportion B decreases from thickness T2 at the edges of portion B to athickness less than thickness T2 at the center of portion B. In someimplementations, as depicted, portions A have tapered thicknesses. Forexample, a thickness of portions A increases from a thickness less thanthickness T2 at top surfaces of portions A to thickness T2 at bottomsurfaces of portions A. In some implementations, portions A have asubstantially planar sidewall surface and a curved sidewall surface, andportion B has a curved top surface and a substantially planar bottomsurface. In furtherance of the depicted embodiment, conductive line 82includes a portion C that extends below the top surface of ILD layer 46and physically contacts via barrier layer 142. Portion C has a thicknessT4 that is less than a sum of thickness T3 and thickness T2 (in otherwords, T4 < T3 + T2). In some implementations, thickness T4 is less thanabout 10 nm. A concave bottom surface of portion C physically contactsvia barrier layer 142, such that a thickness of a center of portion C isgreater than a thickness of edges of portion C. For example, thicknessT4 at the center of portion C is greater than thickness T4 at the edgesof portion C. Conductive line 82 thus has a bottom surface that includesa concave bottom surface portion disposed between substantially planarbottom surface portions. Additional features can be added in theinterconnect structure depicted in portion A of FIG. 4 and some of thefeatures described can be replaced, modified, or eliminated in otherembodiments of the interconnect structure depicted in portion A of FIG.4 .

In FIG. 5 , the planarization process fully removes via bulk layer 152and fully removes a portion of via barrier layer 142, such that via 72does not include via bulk layer 152 and a portion of via barrier layer142 is completely removed from over top surface 134 of via bulk layer132. In such implementations, the planarization process modifies a topsurface of via barrier layer 142 and separates portion B of via barrierlayer 142 into portions B1, such that via barrier layer 142 is separatedinto two discrete portions, where each discrete portion includes one ofportions A and one of portions B1. Portions B1 have curved top surfacesand substantially planar bottom surfaces. Thicknesses of portions B1taper from thickness T2 (adjacent to portions A) to zero. In someimplementations, as depicted, top portions of portions A have taperedthicknesses, and bottom portions of portions A have thickness T2. Forexample, a thickness of top portions of portions A increases from athickness less than thickness T2 at top surfaces of portions A tothickness T2 at some point along a length of portions A. In someimplementations, portions A have a substantially planar sidewall surfaceand a curved sidewall surface. In furtherance of the depictedembodiment, conductive line 82 also includes portion C that extendsbelow the top surface of ILD layer 46, where portion C physicallycontacts not only via barrier layer 142 but also a portion of topsurface 134 of via bulk layer 132. In such implementations, thickness T4is less than or equal to a sum of thickness T3 and thickness T2 (inother words, T4 ≤ T3 + T2). In some implementations, thickness T4 isabout 1 nm to about 10 nm. The concave bottom surface of portion Cphysically contacts via barrier layer 142 and via bulk layer 132, suchthat a thickness of the center of portion C is greater than thethickness of edges of portion C. For example, thickness T4 at the centerof portion C is greater than thickness T4 at the edges of portion C.Conductive line 82 thus has a bottom surface that includes a concavebottom surface portion disposed between substantially planar bottomsurface portions. Additional features can be added in the interconnectstructure depicted in portion A of FIG. 5 and some of the featuresdescribed can be replaced, modified, or eliminated in other embodimentsof the interconnect structure depicted in portion A of FIG. 5 .

In FIG. 6 , the planarization process partially removes via bulk layer152, such that via 72 still includes via bulk layer 152. Theplanarization process modifies a top surface of via bulk layer 152. Forexample, via bulk layer 152 has portions D and a portion E disposedbetween portions D, where top surface of portion E is lower than topsurfaces of portions D and top surface of ILD layer 46. Portions D havesubstantially planar top surfaces, such that thicknesses of portions Dare substantially equal to thickness T3. In some implementations,thicknesses of portions D may be less than thickness T3. In someimplementations, portions D may have tapered thicknesses, similar toportions A of via barrier layer 142 depicted in FIG. 4 and FIG. 5 .Portion E has a concave surface, such that a thickness of a center ofportion E is less than a thickness of edges of portion E. In someimplementations, a thickness of portion E decreases from thickness T3 atthe edges of portion E to a thickness less than thickness T3 at thecenter of portion E. In some implementations, a thickness of portion Edecreases from a thickness less than thickness T3 at the edges ofportion E to another thickness that is less than thickness T3 at thecenter of portion E. In some implementations, the planarization processseparates portion E of via bulk layer 152 into two discrete portions,similar to via barrier layer 142 depicted in FIG. 5 . In someimplementations, via bulk layer 152 does not include different portions,instead having a concave top surface that extends between portions A ofvia barrier layer 142. In furtherance of the depicted embodiment,conductive line 82 also includes portion C that extends below the topsurface of ILD layer 46, except portion C physically contacts via bulklayer 152 and not via barrier layer 142. In such implementations,thickness T4 is less than or equal to thickness T3 (in other words, T4 ≤T3). The concave bottom surface of portion C physically contacts viabarrier layer 142 and via bulk layer 132, such that a thickness of thecenter of portion C is greater than the thickness of edges of portion C.For example, thickness T4 at the center of portion C is greater thanthickness T4 at the edges of portion C. Conductive line 82 thus has abottom surface that includes a concave bottom surface portion disposedbetween substantially planar bottom surface portions. Additionalfeatures can be added in the interconnect structure depicted in portionA of FIG. 6 and some of the features described can be replaced,modified, or eliminated in other embodiments of the interconnectstructure depicted in portion A of FIG. 6 .

The present disclosure provides for many different embodiments.Interconnect structures and corresponding techniques for forming theinterconnect structures are disclosed herein. An exemplary interconnectstructure includes a via disposed in a dielectric layer. The via isconfigured to electrically couple a first interconnect feature and asecond interconnect feature. The via includes a via barrier layer thatphysically contacts the dielectric layer. The via further includes a viaplug disposed between the via barrier layer and the first interconnectfeature, such that the via plug physically contacts the firstinterconnect feature and the dielectric layer. In some implementations,the first interconnect feature is a middle-end-of-line conductivefeature and the second interconnect feature is a back-end-of-lineconductive feature. In some implementations, the first interconnectfeature and the second interconnect feature are back-end-of-lineconductive features. In some implementations, the via plug includestungsten. In some implementations, the via plug includes ruthenium. Insome implementations, the via plug includes cobalt. In someimplementations, the via barrier layer includes titanium. In someimplementations, the via barrier layer includes tantalum. In someimplementations, the via plug is a first via plug portion, and the viafurther includes a second via plug portion disposed over the via barrierlayer. The via barrier layer is disposed between the first via plugportion and the second via plug portion. The via barrier layer isfurther disposed between the dielectric layer and the second via plugportion. In some implementations, a material of the first via plugportion is the same as a material of the second via plug portion. Insome implementations, a material of the first via plug portion isdifferent than a material of the second via plug portion.

An exemplary interconnect structure includes of a multilayerinterconnect (MLI) feature includes a dielectric layer, acobalt-comprising device-level contact disposed in the dielectric layer,and a partial barrier-free via disposed in the dielectric layer over thecobalt-comprising device-level contact. The partial barrier-free viaincludes a first via plug portion disposed on and physically contactingthe cobalt-comprising device-level contact and the dielectric layer, asecond via plug portion disposed over the first via plug portion, and avia barrier layer disposed between the second via plug portion and thefirst via plug portion. The via barrier layer is further disposedbetween the second via plug portion and the dielectric layer. In someimplementations, the first via plug portion and the second via plugportion include tungsten, cobalt, ruthenium, or combinations thereof. Insome implementations, the via barrier layer includes titanium. In someimplementations, the via barrier layer includes a first layer thatincludes titanium and a second layer that includes titanium andnitrogen. In some implementations, wherein the via barrier layerincludes tantalum. In some implementations, the via barrier layerincludes a first layer that includes tantalum and a second layer thatincludes tantalum and nitrogen. In some implementations, the dielectriclayer includes a first ILD layer, a CESL disposed over the first ILDlayer, and a second ILD layer disposed over the CESL. In suchimplementations, the cobalt-comprising device-level contact is disposedin the first ILD layer. In furtherance of such implementations, thepartial barrier-free via is disposed in the CESL and the second ILDlayer, such that the first via plug portion physically contacts the ILDlayer and the CESL and the via barrier layer physically contacts the ILDlayer.

An exemplary method includes forming a via opening in a dielectriclayer. The via opening has sidewalls defined by the dielectric layer anda bottom defined by a contact. The method further includes filling thevia opening by forming a first via bulk layer, forming a via barrierlayer over the first via bulk layer, forming a second via bulk layerover the via barrier layer, and performing a planarization process, suchthat a remainder of the second via bulk layer, the via barrier layer,and the first via bulk layer form the via. In some implementations, thefirst via bulk layer is formed by a selective deposition process, andthe second via bulk layer is formed by a non-selective depositionprocess. In some implementations, the selective deposition process andthe non-selective deposition process are CVD processes. In someimplementations, the planarization process completely removes the secondvia bulk layer.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An interconnect structure comprising: adielectric layer; and a via disposed in the dielectric layer, whereinthe via connects a first interconnect and a second interconnect, andfurther wherein the via includes: a barrier-free via plug and a metalliner, wherein the barrier-free via plug is disposed on the firstinterconnect, the metal liner is disposed on and physically contacts atop surface of the barrier-free via plug, and the metal liner isdisposed between the barrier-free via plug and the second interconnect,wherein a first sidewall of the via is formed by a first sidewallportion of the metal liner and a first sidewall of the barrier-free viaplug and a second sidewall of the via is formed by a second sidewallportion of the metal liner and a second sidewall of the barrier-free viaplug, and the first sidewall portion of the metal liner, the firstsidewall of the barrier-free via plug, the second sidewall of the metalliner, and the second sidewall of the barrier-free via plug physicallycontact the dielectric layer.
 2. The interconnect structure of claim 1,wherein the barrier-free via plug is a tungsten plug and the metal linerincludes titanium.
 3. The interconnect structure of claim 1, wherein thebarrier-free via plug is a ruthenium plug and the metal liner includestitanium.
 4. The interconnect structure of claim 1, wherein thebarrier-free via plug is a cobalt plug and the metal liner includestitanium.
 5. The interconnect structure of claim 1, wherein the metalliner covers an entirety of the top surface of the barrier-free viaplug.
 6. The interconnect structure of claim 1, wherein the secondinterconnect covers a central portion of the top surface of thebarrier-free via plug and the metal liner covers a first end portion anda second end portion of the top surface of the barrier-free via plug,wherein the central portion is disposed between the first end portionand the second end portion.
 7. The interconnect structure of claim 1,wherein the via further includes a via plug disposed on and physicallycontacting the metal liner, wherein the metal liner is between thebarrier-free via plug and the via plug.
 8. The interconnect structure ofclaim 1, wherein the barrier-free via plug has a first thickness, themetal liner has a second thickness, and a ratio of the first thicknessand the second thickness is about 5:1 to about 25:1.
 9. The interconnectstructure of claim 1, wherein the second interconnect extends below atop of the first sidewall portion and the second sidewall portion of themetal liner.
 10. An interconnect structure comprising: a dielectriclayer; a first interconnect disposed in the dielectric layer; and apartial barrier-free interconnect disposed in the dielectric layer,wherein the partial barrier-free interconnect connects the firstinterconnect to a second interconnect, wherein the partial barrier-freeinterconnect includes: a first plug portion disposed on and physicallycontacting the first interconnect and physically contacting thedielectric layer, a second plug portion disposed over the first plugportion, and a barrier layer disposed between the second plug portionand the first plug portion, wherein the barrier layer is furtherdisposed between the second plug portion and the dielectric layer. 11.The interconnect structure of claim 10, wherein the barrier layerconstitutes less than about 2% of a volume of the partial barrier-freeinterconnect, the first plug portion constitutes about 90% to about 99%of the volume of the partial barrier-free interconnect, and the secondplug portion constitutes about 1% to about 10% of the volume of thepartial barrier-free interconnect.
 12. The interconnect structure ofclaim 10, wherein a distance between a top surface of the first plugportion and a top surface of the partial barrier-free interconnect isabout 1 nm to about 10 nm.
 13. The interconnect structure of claim 10,wherein the first plug portion includes ruthenium, the barrier layerincludes titanium, and the second plug portion includes tungsten,cobalt, ruthenium, or combinations thereof.
 14. The interconnectstructure of claim 10, wherein the first plug portion includes tungsten,the barrier layer includes titanium, and the second plug portionincludes tungsten, cobalt, ruthenium, or combinations thereof.
 15. Theinterconnect structure of claim 10, wherein: the first plug portion hasa first thickness, the second plug portion has a second thickness, thebarrier layer has a third thickness; and the first thickness is greaterthan a sum of the second thickness and the third thickness.
 16. Theinterconnect structure of claim 15, wherein a ratio of the firstthickness to the sum of the second thickness and the third thickness isabout 2.5:1 to about 12.5:1.
 17. The interconnect structure of claim 10,wherein the first interconnect is a source/drain contact, the partialbarrier-free interconnect is a source/drain via, and the secondinterconnect is an electrically conductive line of a multilayerinterconnect (MLI) feature.
 18. A method for forming an interconnectstructure comprising: forming an interconnect opening in a dielectriclayer, wherein the interconnect opening exposes a first interconnect;forming a partial barrier-free interconnect in the interconnect opening,wherein the forming the partial barrier-free interconnect includes:depositing a first plug portion over the first interconnect, wherein thefirst plug portion physically contacts the dielectric layer and athickness of the first plug portion is less than a depth of theinterconnect opening, depositing a barrier layer over the first plugportion, depositing a second plug portion over the barrier layer,wherein the second plug portion and the barrier layer fill a remainderof the depth of the interconnect opening, the barrier layer is disposedbetween the first plug portion and the second plug portion, and thebarrier layer is disposed between the second plug portion and thedielectric layer, and performing a planarization process; and forming asecond interconnect over the partial barrier-free interconnect, whereinthe partial barrier-free interconnect connects the first interconnectand the second interconnect.
 19. The method of claim 18, wherein theplanarization process recesses the second plug portion below a topsurface of the dielectric layer.
 20. The method of claim 18, wherein theplanarization process completely removes the second plug portion below atop surface of the dielectric layer.